1. Field of the Invention
The present invention relates to a sheet feeding apparatus used with an image forming system such as a copying machine, laser beam printer and the like, and more particularly, it relates to a sheet feeding apparatus having a feeding member (refer to as "feed roller" hereinafter) and a friction member (refer to as "separating pad" hereinafter).
2. Related Background Art
In the past, a sheet feeding apparatus having a feed roller and a separating pad has been known. In such conventional sheet feeding apparatus, the sheet is fed while frictionally contacting the sheet with the separating pad biased toward the feed roller, and the feeding of the next sheet is prevented by abutting the leading edge of the next sheet against the separating pad.
However, in the above-mentioned conventional sheet feeding apparatus, since the whole area from the leading edge to the trailing edge of the sheet being fed frictionally contacts the separating pad, the frictional resistance in the sheet feeding movement is increased to cause the premature wear of the feed roller, thus shortening the service life of the feed roller, and further, to cause the excessive wear of the separating pad, thereby worsening the sheet separation ability of the separating pad resulting in the double-feed of sheets.
Further, in order to handle thicker sheets or sheets hard to bend (or curl) such as cards or envelopes, sheet feeding apparatuses as disclosed in the U.S. Pat. Nos. 1,919,238 and 3,640,524 have been proposed. In such conventional sheet feeding apparatuses, a separating pad is arranged with a predetermined inclined angle with respect to a sheet feeding direction at a position where the leading edge of the sheet fed by a feed roller is abutted against the separating roller. Further, a sheet feeding force provided by the feed roller overcomes a force that the separating pad tends to retain the leading edge of the sheet, whereby the top sheet slips on the separating pad to separate therefrom, thus feeding the top sheet. On the other hand, the next and the other sheets are not subjected to a feeding force greater than a friction force between the sheets, and, accordingly, these sheets are prevented from being fed and are remain stationary in the condition that the leading edges of these sheets are abutted against the separating pad.
However, in the above-mentioned conventional sheet feeding apparatus of the type wherein the sheets are separated by abutting the leading edges of the sheets against the separating pad, if the leading edge portion of the sheet is curled to increase an angle .theta. between the leading edge of the sheet and the separating pad as shown in FIG. 18, the friction force between the leading edge of the sheet and the separating pad will be greater than the friction force between the sheet and the feed roller, with the result that the feed roller frequently slips on the sheet to prevent the feeding of the sheet.